Though none of his arresting concepts have yet come to fruition, Belgian architect Vincent Callebaut may be the most prolific designer of fantastic future cities. Callebaut designed the Lilypad, basically a giant ocean-bound football stadium carpeted with foliage, as an unmoored refugee camp for people displaced by rising seas and other impending environmental hazards.

Stupefaction Factor: 8. While Callebaut doesn't propose a specific size for his Lilypad, he guesses that each one could house 50,000 refugees, which is equivalent to the population of a city the size of Cheyenne, Wyoming. Imagine a random assortment of disgruntled climate refugees drifting about the world's oceans in a tree-covered half pipe.

Fantasy Factor: 9. In the unlikely event that everyone on Earth went crazy and decided that this would be the best way to house those affected by environmental problems, we would still have to figure out how to fund the thing. And the only people with enough money to launch the project probably depend on environmental destruction for their income.

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